Sintering Characteristics of Al–Pb/Fly-Ash Metal Matrix Composites

Aluminum–lead/10 wt% fly-ash powder mixtures containing 0–20 wt% lead (Pb) were prepared. These powder mixes were compacted in the pressure range of 200–400 MPa by single action die compaction process. The prepared compacts were sintered in the temperature range of 500, 530, 560 and 590 °C in an argon gas atmosphere for duration of 45 min. For the sintered compacts, the sintered density, hardness and compressive strength were reported. Sintered density, hardness and compressive strength increased with the increase in compaction pressure. Sintered density increased whereas the hardness and the compressive strength decreased with the addition of Pb.     

Titanium–hydroxyapatite composite biomaterial for dental implants

Abstract

The objective of the present study was to investigate high velocity compaction of titanium powder and to prepare a dense composite biomaterial of titanium and hydroxyapatite with the purpose of forming dental components with improved early healing properties. A high purity titanium powder was compacted using high velocity compaction to study the density distribution. Then, a titanium–hydroxyapatite composite was prepared by mixing titanium powders and hydroxyapatite grains. Dental implant components were formed from the high velocity compacted specimens, exposing the hydroxyapatite grains at the component surface. The green density reached more than 98·5% after more than one impact. The composite was heated to 500°C, enough to bind the titanium grains, but to avoid observable reactions. Compacted pure titanium could be sintered to full density. The heated composite material reached 99% density, no reaction was observed between titanium and hydroxyapatite, and the composite material could be formed into dental implants.     

Impact of High Pressures during the Compaction of Zirconia Nanopowder on Material Structure Formation

The influence of compaction pressure during semidry compaction in a steel mold of zirconia powder partially stabilized by yttria on the phase composition and microstructure of formed compacts, as well as samples sintered at 1400°C for 2 h, is investigated. An aqueous solution of polyvinyl alcohol is selected as a temporary manufacturing binder. The yttria content in the powder synthesized according to the sol–gel technology (the deposition by an aqueous-ammonia solution from aqueous ethanol solutions of corresponding reagents with the agar-agar additive) is 3.2 mol % according to the X-ray fluorescent analysis data. The results of studying the compacts and sintered samples by Raman spectroscopy, optical microscopy, and atomic force microscopy are presented. It is established that an increase in their density is not monotonic. There is the critical range of compaction pressures P = 400–450 MPa, in which the porosity, pore shape and sizes, microstructure, and phase composition of the material vary abruptly. A monoclinic phase, the content of which varies upon varying P, is fixed in compacted samples along with tetragonal zirconia. Material grain grinding is associated with the destruction of agglomerates and actively occurs in range P = 350–550 MPa. A similar effect when studying the compaction process of nanopowders of zirconia is also noted by other researchers, who assumed that the response of the nanopowder system on the pressure effect is associated with the influence on the aqueous component (the temporary manufacturing binder in this case) and is caused by the transition of one form of water into another one at 10–25°C and a pressure of 400–700 MPa.

     

铁粉特性对温压生坯密度的影响

从铁粉类型、粒度组成、化学成分和粉末显微硬度等因素对温压生坯密度的影响情况进行了系统试验,结果表明,通过控制粉末形状、粒度分布、化学成分等因素,温压可获得高压坯密度,在本试验中,经过处理的国产粉温压压制密度最高可达７．３０ｇ／ｃｍ＾３,接近国外粉末压制密度。     

Characterization,Physical and Mechanical Behavior of Sintered Atomized Iron–Zinc Stearate Composite

Powder metallurgy is an effective method to process the iron component in near net shape. In this paper, the influence of particle size, lubricant and compaction load on the physical and mechanical properties of the sintered iron–zinc stearate composite sample has been investigated. Atomized iron powders of particle size 100–200 and 200–300 mesh with zinc stearate 2.5, 5.0 and 7.5 wt% were used for preparing the samples. Green samples were prepared by cold compaction at various loads of 200, 180 and 160 KN and the sintering is done at 500 °C. The physical properties and the mechanical properties such as density, hardness and compression strength have been measured for the sintered samples. Scanning electron microscope was used to characterize the atomized iron powders and the sintered samples. It were confirmed that the shape of atomized iron powder particles were irregular, dendritic and acicular. Energy dispersive spectroscopy was used to identify the elemental compositions of powders and the sintered samples. Taguchi (L₁₈) method was effectively used to develop the regression model and describe the contribution of the input parameters in compressive strength, density, and hardness. The highest effect on density was powder particle size followed by compaction load and lubricant wt%. The Hardness value increased with increase in the powder particle size and compaction load and decreases with increase in the lubricant wt%. The compression strength increased with increase of compaction load and decrease of lubricant wt% and particle size.     

Tensile and fatigue properties of cold and warm compacted Alumix 431 alloy

Abstract

In this experimental study, tensile and fatigue properties of the Alumix 431 alloy (Al, Zn, Mg and Cu alloys) produced using the conventional press and sinter processes in different pressures and temperatures are investigated. The results clearly showed that the warm compacted specimens can reach the mechanical properties of the cold compacted ones under less pressure. In the fatigue tests it was observed that fracture started from large pores as shown in all scanning electron microscope (SEM) examinations and ductile fracture occurred. 85% of the 180 MPa/80°C and 77% of the 230 MPa/RT specimens fractured at the machined surface. Tensile and fatigue properties of warm compacted (180 MPa/80°C) and cold (230 MPa/RT) compacted specimens are almost equal at these same densities. This result indicates the economic benefit of warm compaction by the much lower applied compaction pressure.     

Nanostructure Cu–Cr alloy with high dissolved Cr contents obtained by mechanical alloying process

Abstract

A nanostructural solid solution of Cu–Cr was prepared by the mechanical alloying process. Three mixtures of Cu powders with 1, 3 and 6 wt-%Cr powders were milled under 250 rev min^?1 for different milling times of 4, 12, 48 and 96 h. The mixtures were subsequently compacted and sintered at 450, 600 and 750°C for half an hour. Milled powder mixtures were examined by X-ray diffraction technique, which showed the presence of nanoscale crystallites in the samples and the decrease of lattice parameter of Cu crystals. Sintered powders were investigated by optical microscope and their hardnesses were measured by microhardness. Results showed increasing trends in hardness of the compacted powder mixtures with increasing milling time. Sintering temperature had also evident effects on the behaviour of powder mixtures. As sintering temperature increased, microhardness increased and a peak appeared then a decreasing trend was observed.     

Fabrication,microstructures and properties of 50 vol.-% SiCp/6061Al composites via a pressureless sintering technique

Commercial F500 SiC powder and 6061 Al powder were chosen to fabricate the 50?vol.-% SiCp/6061Al composites via pressureless sintering. Effects of pre-treatment of the SiC powder and sintering temperature on the microstructures and properties of the composites were studied. Densification mechanism and interfacial reaction of the composites were also investigated. The results show that the composites have a high sintering ability and a low interfacial reaction activity. The density, bending strength and thermal conductivity of the composites are all sensitive to the sintering temperature. The composites sintered at 680°C are nearly fully dense and have the following optimal properties: the relative density of 98.5%, the bending strength of 495?MPa, the TC of 153?W/(m?K) and the coefficient of thermal expansion of 8.1?×?10^?6/°C (50–100°C), which are superior to most of the SiCp/Al composites of the similar composition reported previously.     

粘结化铁基粉末的高速压制成形与烧结行为研究

研究了采用粉末改性处理和高速压制相结合的技术制备高密度铁基粉末冶金材料的工艺。所用的粘结化铁基粉末的名义成分(质量分数)为Fe-1.5Ni-0.5Cu-0.5C;重点研究了压制能量和粉末塑化改性对压坯密度的影响,以及高密度压坯的烧结致密化行为。结果表明:粘结化铁基粉末具有较高的流动性(25.1s/50g)和松装密度(3.2～3.4g/cm3)。未经塑化改性处理的粉末随着压制速度的增加,压坯密度提高缓慢,在8.7m/s高压制速度下,压坯密度为7.37g/cm3。塑化改性处理粉末具有优异的塑性变形能力,压坯密度随着冲击能量的增加而迅速增大,在6.2～8.7m/s的压制速度范围内,压坯密度为7.07～7.62g/cm3。经过8.7m/s高速压制和1 150℃烧结后,烧结体密度达到7.51g/cm3,相对密度为96.5%。     

压制方式和烧结工艺对置氢Ti6Al4V粉末烧结体组织和性能的影响

采用磁脉冲成形和模压成形2种方法对置氢Ti6Al4V粉末进行轴向压制,然后在保护气氛下烧结,研究压制方式和烧结工艺对烧结体真空退火后组织/性能的影响.结果表明:磁脉冲压实的不同氢含量粉末坯体烧结并真空退火后的相对密度、硬度和抗压强度分别比传统模压500 MPa下压制的高8%～13%、9～17 HRA和254～1033M...